If you are just going for the day I would recommend checking out rental car prices. Weekend rates for a rental car are often from $18 to $25 including taxes. The only downside is parking can be expensive in the bigger cities you mentioned like SFO, SEA, LAX etc, but if you want some flexibility and to get out of the major cities they are a great option. I live in SLC and so if you decide to come out this way I can give you some tips. Although it sounds like you are looking more for a beach, which we don't have.